Washington: An influential US Senator is believed to have put on hold the confirmation of President's nominee for ambassador to Pakistan in the Senate, in an apparent protest against continued detention of a Pakistani doctor who helped CIA trace Osama bin Laden.

Rand Paul, the Republican Senator, media reports said, has objected to the nomination of Rick Olson, who was earlier nominated by Barack Obama as his envoy to Pakistan. The hold on ambassadorial nominee comes at a critical time when the US is trying to build up its relationship with Pakistan with the reopening of the ground lines of communication and also when the US is preparing for the withdrawal of its troops from Afghanistan.

The move has upset friends of Pakistan in Washington and many in the Administration as the Senate was quick in unanimously confirming the nomination of the US Ambassador-designate to Afghanistan, while that for Pakistan has been blocked for now.

The confirmation hearing for both was held last week. While Senator Paul, who has also a pending legislation in the Senate to suspend US aid to Pakistan unless, Dr Shakeel Afridi, the doctor who helped CIA track Laden, is not released.

Senator John Kerry, Chairman of the Senate Foreign Relations Committee, has said that the Ambassadorial position in Pakistan is too important to remain vacant at this point of time.

"This is a complicated relationship that demands constant attention. We've been working day and night with Pakistan to build a stable economy and strengthen our engagement with its people, and after such a tumultuous year, this is exactly the wrong time to leave such an important post vacant," Kerry said.

"I can't think of a good reason for doing so. We recognised the importance of this position and expedited it out of committee and I urge the Senate to move this nomination through as quickly as possible when we return from the recess," he added.

"While we are disappointed that Ambassador Olson was not confirmed on Thursday, we are working closely with the Senate to ensure a swift and smooth confirmation process and hope Ambassador Olson will assume this critical post soon," a State Department official said.

Afridi was on May 24 sentenced to 33 years in jail after he was found guilty of treason. The tribal court later said that he was convicted for helping and funding the banned Lashkar-e-Islam militant group and it did not have the jurisdiction to take up charges that Afridi had worked for the CIA. (Agencies)